How 529 college savings math works
Named for Section 529 of the tax code, these plans are sponsored by states and share one core deal: money you contribute is invested, grows free of federal tax, and comes out federal-tax-free when spent on qualified education expenses — tuition, fees, books, and generally room and board. Many states sweeten the deal with a state-tax deduction or credit. The planning problem is a race between two compounding curves: your savings growing at an investment return, and the college bill growing at education inflation. Because published tuition has historically risen faster than general consumer prices, this calculator gives the bill its own inflation rate rather than reusing a generic CPI figure. Enter today's all-in annual cost — the College Board's annual Trends in College Pricing report publishes current averages by school type — and the tool projects what the years your student will actually be enrolled will cost.
The two formulas
Total cost = Σk=0…Y−1 C₀ × (1 + g)t+k × cover%
PMT = (FVtarget − B₀(1 + i)n) × i ÷ ((1 + i)n − 1)
where C₀ is today's annual cost, g education inflation, t years until enrollment, Y years of college, B₀ the current balance, i the monthly rate (annual return ÷ 12), and n the number of months left. The first line inflates each college year separately from today; the second is the standard annuity solve for the end-of-month contribution that grows, together with the current balance, to exactly the target by enrollment.
Worked example
Take the default scenario: a family 10 years from enrollment with $10,000 saved, contributing $300/month at a 6% expected return, against a school costing $25,000/year today with 5% education inflation:
| Step | Amount |
|---|---|
| Money you put in$10,000 already saved + $300/month for 10 years | $46,000 |
| + Investment growth6% annual return, compounded monthly (i = 6% ÷ 12) | $21,358 |
| = Projected 529 balance at enrollmentwhat the plan holds when college starts in 10 years | $67,358 |
| Projected 4-year bill$25,000/year today, inflated at 5% — year 1 alone is $40,722 | $175,518 |
| = Shortfall — the plan covers 38.4%fully funding the bill would take about $960/month instead of $300 | $108,161 |
Computed with this calculator's default settings — open the tool above and you'll see the same numbers, then swap in your own timeline and costs.
Why the funding gap is the number that matters
A projected balance means little on its own — the question is what share of the actual, inflated bill it covers. That is why this calculator leads with the funding percentage and the required monthly contribution. Small changes compound: starting a few years earlier, or nudging the contribution up when the required figure drifts away from your plan, matters far more than chasing an extra point of return. And a 529 does not have to carry the whole load. Grants, scholarships, current income, and student earnings routinely cover a large share of real-world costs, which is why the calculator lets you target a percentage of the bill rather than all of it. Flexibility has also improved: under the SECURE 2.0 Act, money stranded in a long-held 529 can, within limits and subject to conditions, be rolled into the beneficiary's Roth IRA — softening the old fear of overfunding.
The savings side of this tool is ordinary compound growth — explore it in more depth with thecompound interest calculator, work the same solve-for-the-payment logic on any target with thesavings goal calculator, or compare education saving with the other big tax-advantaged account using theHSA calculator.
Frequently asked questions
What is a 529 plan?
A 529 plan is a state-sponsored investment account built for education savings. Money inside grows free of federal tax, and withdrawals are also federal-tax-free when spent on qualified education expenses — tuition, fees, books, and generally room and board at eligible institutions. Contributions are made with after-tax dollars (there is no federal deduction), though many states offer a state income-tax deduction or credit for contributing. Nearly every state sponsors at least one plan, and you can usually enroll in any state’s plan regardless of where you live or where the student ultimately attends school.
What if my child doesn’t go to college?
You have several outs. You can change the beneficiary to another eligible family member — a sibling, cousin, or even yourself — without tax consequences. You can simply withdraw the money: contributions come back tax- and penalty-free, but the earnings portion of a non-qualified withdrawal is subject to ordinary income tax plus a 10% federal penalty. And under the SECURE 2.0 Act, limited amounts can be rolled from a long-held 529 into the beneficiary’s Roth IRA, subject to conditions such as account age, annual contribution limits, and a lifetime cap.
How much should I save each month?
It depends on the time left, your expected return, the cost you are targeting, and the share of it you intend to cover. This calculator solves the annuity math exactly: with the default inputs — 10 years out, $10,000 saved, a $25,000/year cost inflating at 5%, and a 6% return — fully funding four years takes about $960/month. Many families deliberately target a smaller share, such as a third or half of the projected bill, and plan on aid, current income, and student earnings for the rest.
Do 529 plans hurt financial aid?
Less than most families fear. Under the federal aid formula, a 529 owned by a parent (or by a dependent student) is reported as a parental asset on the FAFSA, and parental assets are assessed at a maximum of 5.64% in the Student Aid Index calculation — far gentler than the treatment of student income or student-owned assets. In other words, each $10,000 of parent-owned 529 money raises the SAI by at most $564. See studentaid.gov for how the federal formula works; individual colleges using their own aid formulas may treat assets differently.
Can I use a 529 for K-12 or other education?
Federal law allows tax-free 529 withdrawals for elementary and secondary school tuition up to an annual per-student limit, and for certain apprenticeship costs and limited student-loan repayment. But state treatment varies: some states do not consider K-12 tuition a qualified expense, so a withdrawal that is federal-tax-free could still trigger state tax or recapture of a state deduction. Check your own plan’s rules and the IRS guidance before using 529 money for anything other than post-secondary education.
Sources
- IRS — 529 Plans: Questions and Answers
- College Board — Trends in College Pricing (current published cost averages)
- Federal Student Aid — How Aid Is Calculated (Student Aid Index)
The official figures this page quotes are drawn from the primary sources above — check them (or a qualified professional) before relying on a result.
Disclaimer: This calculator is foreducation and illustration only. Investment returns are not guaranteed, education inflation varies by school and state, and 529 tax rules — including state deductions, K-12 treatment, and Roth rollover conditions — change and differ by state. All cost figures are your inputs, not published averages. Nothing here is investment, tax, or financial-aid advice; consult your plan documents or a qualified professional before making decisions.